Electric heating coil structure



2 Sheets-Sheet l ATTORNEY May 17, 1955 L. DUDA, JR

ELECTRIC HEATING c011. STRUCTURE Filed April 23, 1952 i TI[M y 7 5 L.DUDA, JR 2,708,704

ELECTRIC HEATING COIL STRUCTURE Filed April 23, 1952 2 Sheets-Sheet 2mil A TTORNE X Unite 1 2,708,704 ELECTRIC HEATING COIL STRUCTURE LouisDuda, Jr., Chicago, 111., assignor to Lindberg Engineering Company,Chicago, IlL, a corporation of Illinois Application April 23, 1952,Serial No. 283,801 Claims. (Cl. 219-10379) This invention relates to anelectric heating coil structure, and more particularly to an inductionheating coil structure for heating the edge portion only of a workpiece.

According to current practices, it is dimcult to shape the coils toobtain the desired distribution of the inductive heating effect withoutcreating hot spots Where the metal is overheated. It is also diflicultto provide a coil capable of suflicient loading to heat the work rapidlyenough so that the heating will be confined to the desired edge portionsof the work and will not have time to extend the heated area byconduction through the work.

It is one of the objects of the present invention to pro vide a heatingcoil structure in which the heating effect is confined to a narrow edgeportion only of the work.

Another object is to provide a coil structure whose impedance is low sothat the coil is capable of high loading and therefore rapid heating.

Still another object is to provide a coil structure which is extremelysimple and inexpensive to manufacture and which can be made insubstantially any desired shape to produce any desired distribution ofthe heating efiect.

A further object is to provide a coil structure in which cross-flowsbetween portions of the coil are eliminated to eliminate hot spots.

The other objects and advantages of the present invention may be moreclearly seen by reference to the attached drawings, in which:

Figure 1 is a perspective view of one form of coil structure embodyingthe invention;-

Figure 2 is a transverse section through the coil struc ture of Figure1;

Figure 3 is a front elevation;

Figure 4 is a sectional view illustrating distribution of flux;

Figure 5 is a view similar to Figure 2 illustrating an arrangement forheating both edges of a strip;

Figure 6 is a front elevation of an alternative coil structure;

Figure 7 is an end elevation of still another coil structure;

Figure 8 is an end elevation of a multiple coil structure, and

Figure 9 is a front elevation of still another coil structure embodyingthe invention.

As shown in Figures 1 to 3, the coil structure is adapted to heat theedge portion only of a relatively narrow elongated strip 10 either in acontinuous operation or in sequential operations on separate pieces.

The coil structure includes a pair of bus bars 11 which are adapted tobe connected to a source of heating current, such for example, as astandard inductive heating generator. The bus bars 11 are mountedclosely adjacent to each other in parallel relationship and normallyproject horizonally from the front of the generator to carry the coilstructure at the front side of the generator Where it is convenientlyaccessible.

States Patent 0 The coil structure, itself, comprises a pair ofidentical plate members 12 formed of conducting material, such ascopper, and which, as shown in Figures 1 to 3, are flat relatively thinplates. Each of the plates is formed with a pair of upstanding legmembers 13 which lie closely adjacent to each other in parallelrelationship and which are connected to the bus bars 11 by welding,brazing, or the like. This not only establishes an electrical connectionbetween the plate members and the bus bars but supports the platemembers from the bus bars in parallel spaced relation to receive thework piece 10 between them. Each plate member is further formed with anenlarged window 14 defined by a strip like body portion extendingcompletely around the window and joined to the legs 13. in this way,each plate member is split to define a single turn loop and the loopsfor the two plate members are con-v nected in parallel to the bus bars11.

The work piece 10 which is intended to have only one edge portionthereof heated is positioned between the plate members as shown inFigures 2 and 4, so that the upper edge thereof lies in registry withthe windows 14 in the plate members. For continuous heating, the stripmay be drawn continuously between the plate members on any suitableguides or for individual pieces the pieces may be placed between theplate members and removed after treating.

As shown in Figure 4, an instantaneous polarity may be assumed in whichthe top conductors and the plate members are positive and the bottomconductors are negative. Assuming that positive potential will causeflow of current into the plane of the paper each of the upper conductorsindicated at 15, will produce individual fluxes in the direction of thedotted arrows 16.

The lower conductors indicated at 17 will at the same time produceindividual fluxes as shown by the dotted arrows 18. These fluxes allbeing in the same'direction produce an overall flux for the entire coilformed by the two parallel turns as indicated by the dotted arrows 1?.It has been found that these fiuxcs apparently tend to out only the edgeportion of the work piece 10 so that a high degree of heating isproduced in a relatively narrow part of the work piece at its edge andthe body portion of the work piece remains cool. Also, because the coilsare both single turn loops connected in parallel their impedance isrelatively low and they are capable of very substantial loading toproduce an extremely rapid heating effect. Supporting of the coils inparallel through the legs 13 eliminates any cross flows between thecoils which might produce hot spots in the work and when the window 14is of symmetrical shape a uniform symmetrical heating efiect isproduced.

in one coil structure made substantially in accordance with Figures 1 to3 for treating the edges of steel strips through approximately 5 inchesof the edge portion and in which the strips were approximately ,2 inchthick, it was found that a loading of 25 kw. could be used. in thisoperation the strip was heated for a distance of approximately inch fromits edge to a very high temperature in less than one-half second.

When it is desired to heat both edges of a strip the construction asshown in Figure 5 may be employed. Thisembodies a pair of plates 21constructed substantially exactly like the plates E2 of Figure l, andconnected in the same manner to bus bars 22. The plates 21 haverelatively large windows 23 therein whose width is greater than thewidth of the work piece 24 to be treated. The work. piece is positionedbetween the plates such that both edges thereof fall within'the line ofthe windows as shown. When current is supplied to the plates 21 the fluxpattern similar to thatshown in Figure 4 will be produced except thatthe flux lines will divide and pass over both edges of the work piece.Therefore, both v u edges of the work piece will be heatedsimultaneously in the same manner as the single edge of the Work piece10 is heated in operation of Figures 1 to 4.

Figure 6 illustrates a construction wherein spaced portions of a workpiece are heated simultaneously. As shown in this figure, plates areprovided which are similar to the plates 12 of Figures 1 to 3 exceptthat two spaced windows 26 and 27 are formed therein. The work piece maybe an elongated rod or tube 23 which extends between the plates 25 withits edges exposed in the windows 26 and 27. When the plates are suppliedwith current in this construction only those portions of the work piecewhich are exposed in the windows 26 and 27 will be heated and only theedge portions of the work piece will be heated.

If it is desired to case harden spaced portions on a shaft or tube suchas 2d, the tube or shaft may be rotated while the plates are energizedso that the surface thereof which is exposed in the windows 27 will beheated throughout the full periphery of the work piece. way spacedportions on a shaft or tube can easily be case hardened. With similarlyshaped plate members provided with windows of the proper size and shapeany other desired type of work piece can be treated at spaced pointstherein.

Figure 7 illustrates a construction which is particularly adapted tobrazing seams in tubes or the like. As shown in this figure, platemembers 2% are provided with straight parallel legs attached to bus bars31 in the same manner as the legs 13 of Figure l are attached to the busbars 11. Below the legs, the plates are curved outwardly as indicated at32. in opposite directions to fit over a tube 33 in spaced relationshiptherewith. The body portions 32 are formed with windows 34 with whichthe upper part of the tube registers when the tube is placed between theplates.

When current is supplied to the plates the upper edge portion of thetube which registers with the windows 34 will be heated and may besupplied with brazing material indicated at 35, to form a brazed seam inthe tube. By curving the plates outwardly as indicated at 32, relativelylarge work pieces can be accommodated with a minimum size and spacing ofplates so that concentration of the heating flux in the desired areascan be controlled.

For accommodating several work pieces at the same time a construction asshown in Figure 8 may be employed. In this figure, bus bars 35 support aplurality of plate members 37, three such members being shown. The platemembers are spaced apart to receive work pieces 38 between each pair ofplate members and the plate members are formed with windows 39registering with the edge portions or" the work pieces. This construction functions in the same manner as described above in connectionwith Figures 1 to 4, but is capable of treating two or more work piecessimultaneously.

Figure 9 illustrates arrangement for treating a larger number ofcontinuous elongated work pieces simultaneously in slightly differentmanners. As shown in this figure, plates 41 are provided and are formedwith four windows 42, 43, 44 and Elongated strips 46 are passedtransversely between plates 1 with their edges exposed in the windows 42and 45 as shown so that one edge of each strip will be heated. Similarstrips 47 which are narrower than the windows 43 and 44 are passedbetween the plates in registry with the windows 43 and 44 and with bothedges of the strips exposed in the windows so that both edges will beheated.

It will be readily understood that for ditferent types of work platescan easily be shaped to provide the desired distribution of heat. Itwill also be understood that the plates can be water cooled in the usualway by brazing or otherwise securing water circulating tubes thereto forcirculation of cooling water in heat transferring relationshiptherewith. Therefore, while several dilferent coil In this illstructures have been illustratedand described, it is not intended thatthese should be taken as an indication of the scope of theinvention,'reference being had for this purpose to the appended claims.

What is claimed is:

1. An electric heating coil structure comprising a plurality ofrelatively thin plates of conductive material mounted in spaced relationto receive work to be heated between them, the plates being shaped tolie substantially parallel to opposite sides of the Work, each of theplates being split to form a complete single turn coil lying wholly atone side of the work and the splits on the plates being narrow at pointswhere no heating is desired and being enlarged at at least one point toform registering windows to register at least partially with the workwhen it is between the plates, and conductor legs on each of the plateslying closely adjacent to each other and connecting the coils formed bythe plates in parallel to a source.

2. An electric heating coil structure comprising a pair of fiat platesof conductive material mounted in parallel spaced relationship toreceive work to be heated between them, each of the plates being splitto form a single turn coil and the splits in the plates being widened atat least one point to form windows which are in registry with eachother, and conductor legs on each oi the plates lying closely adjacentto each other and connecting the coils formed by the strips in parallelwith each other.

3. An electric heating coil structure comprising a pair of flat platesof conductive material mounted in parallel spaced relationship toreceive work to be heated between them, each of the plates being formedwith an enlarged body portion and a pair of closely spaced leg portions,the body portion being separated to form with the legs a single turncoil with the separation at at least one point being relatively wide todefine a window, the plates being arranged with the windows therein inregistry, and conductors connecting the leg portions of the plates inparallel with each other.

4. An electric heating coil structure comprising a pair of flat platesof conductive material mounted in parallel spaced relationship toreceive Work to be heated between them, each or" the plates being formedwith an enlarged body portion and a pair of closely spaced leg portions,the body portion being separated to form with the legs a single turncoil with the separation at a plurality of spaced points beingrelatively wide to define spaced windows, the plates being arranged withthe Windows therein in registry, and conductors connecting the legsportions of the plates in parallel with each other.

5. An electric heating coil structure comprising a pair or" parallelclosely spaced conductor bars, a pair of single turn coils each havingclosely spaced legs connected to the conductor bars respectively withthe legs of the two coils spaced from and parallel to each other so thatthe coils are connected to the conductor bars in parallel, the coilsdefining open registering windows spaced from the conductor bars by thelegs, the coils being spaced apart to receive the work to be heatedbetween them with at least a portion of the work lying between thewindows and with the window forming portions of the coils lyingsubstantially parallel to the work on opposite sides thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,428,303 Wood Sept. 30, 1947 2,582,955 Body Jan. 22, 1952 FGREIGNPATENTS 616,063 Great Britain Jan. 14, 1949 957,283 France Feb. 15, 1950

